This proposal describes a five-year mentored physician-scientist training program for the candidate to develop his proficiency in the scientific method, mentorship, writing and grantsmanship. Furthermore, the candidate will acquire independent skills in areas of genome editing, genotype-phenotype analysis and cardiac calcium signaling. This will be accomplished in the context of investigating the role of late sodium current in dilated cardiomyopathy. Late sodium current arises from dysfunctional human gated voltage channels and is known to contribute to other cardiac disorders, but the role of late sodium current in dilated cardiomyopathy remains incompletely understood and largely based on animal models. The hypothesis examined here is that enhanced late sodium current results in mechanical and electrical dysfunction in dilated cardiomyopathy by further aggravation of calcium handling and gives rise to delayed after depolarizations. This proposal aims to examine the cellular mechanism of disease of the late sodium current using human induced pluripotent stem cell derived cardiomyocytes (iPSC-CM). All iPSC-CMs in this proposal will be matured using a novel protocol that augments electrical, mechanical and cell signaling properties of iPSC-CMs closer to properties of adult cardiomyocytes. First, cardiomyocytes from three dilated cardiomyopathy patients with SCN5A variants will be examined to determine if the late sodium current is the driving mechanism of cardiomyopathy in those cases. Subsequently, similar experiments will be repeated in iPSC-CMs from patients with dilated cardiomyopathy not caused by variants affecting sodium channel loci. Late sodium channel current will be blocked and enhanced to evaluate the impact on mechanical and electrical phenotype. Lastly, the role of the ryanodine receptor in mediating delayed after depolarizations will be tested to determine if this cellular mechanism is the pathway by which the late sodium current contributes to arrhythmia. This will uncover genotype-specific disease mechanisms related to late sodium current that may explain heterogeneity in electrical and mechanical dysfunction across cases of dilated cardiomyopathy and identify novel therapeutic targets. This proposal takes a novel approach of using iPSC-CM derived from patients with multiple causative variants of DCM to study differences in disease mechanism. Results of these experiments will provide preliminary data and expertise to future work examining role of other genetic variants in influencing electrical and mechanical dysfunction in DCM and identifying genotype-specific therapies for patients with cardiomyopathy. These investigations will be performed under the guidance of the candidate?s advisory committee, which possesses significant expertise in the skills applied in this proposal. The environment at Stanford is ideal for this research proposal and provides a rich setting for the candidate?s growth as an independent investigator. At the culmination of this proposal, the candidate will have the expertise and preliminary data to compete for R01 funding and pursue a career as a physician scientist.